1. Field of the Invention
The present invention relates to a method and a system for charged particle beam exposure.
2. Description of the Related Art
FIG. 9 schematically shows the construction of a conventional charged particle beam exposure system.
In chamber 10, electron beam EB0 emitted from electron gun 11 has its cross section shaped by the rectangular aperture of aperture stop 12, passes through electromagnetic lens 13 to be substantially paralleled and is incident on blanking aperture array mask 14. Blanking aperture array mask 14 has a number of, for example, 1024 apertures being two-dimensionally arranged. FIG. 10 shows apertures 141 to 143 among the apertures. By apertures 141 to 143, electron beam EB0 is shaped into multiple beams. At the edges of apertures 141 to 143 of blanking aperture array mask 14, paired electrodes E1 and G1, paired electrodes E2 and G2 and paired electrodes E3 and G3 are formed, respectively. Electrodes G1, G2 and G3 are set at 0 V by being connected to a non-illustrated common grounding conductor. For example, when electrodes E1 and E3 are set at 0 V and electrode E2 at 15 V, as shown in the figure, electron beams EB1 passing through apertures 141 and 143 are not deflected and electron beam EB2 passing through aperture 142 is deflected.
In FIG. 9, due to the influence of electromagnetic lens 13, electron beams EB1 converge to the position of the aperture formed in aperture stop 15 disposed below and passes through the aperture, whereas electron beam EB2 is intercepted by aperture stop 15. Blanking deflector 16 disposed between blanking aperture array mask 14 and aperture stop 15 is used in order that electron beams EB1 and EB2 having passed through blanking aperture array mask 14 are all intercepted by aperture stop 15 at high speed. Electron beams EB1 having passed through the aperture of aperture stop 15 are converged by objective lens 17 onto a non-illustrated wafer mounted on movable stage 18. Thus, a pattern corresponding to a binary potential pattern to be applied to electrodes E1 to E3 of blanking aperture array mask 14 is projected onto the wafer with demagnification. Major deflector 19 and sub-deflector 20 disposed above movable stage 18 are provided for causing electron beams EB1 to scan on the wafer.
Electrodes E1 to E3 of blanking aperture array mask 14 are supplied with a drive voltage pattern into which a signal pattern outputted from pattern generator 21 has been converted by BAA driver 22.
Electron beam exposure, which is performed through scanning by electron beams, requires a longer processing time than optical exposure. To reduce the processing time, the transfer rate of each bit of the output of pattern generator 21 is set at high bps such as 400 Mbps. For this reason, variation among bits in signal propagation delay time from the output of pattern generator 21 to the electrodes of blanking aperture array mask 14 affects the accuracy of the exposure pattern on the wafer.
Therefore, conventionally, in the adjustment stage of the charged particle beam exposure system, electron beams EB1 are captured by Faraday cup 23 mounted on movable stage 18 and is provided to delay time detecting circuit 24 as current I, while the output of pattern generator 21 is provided to delay time detecting circuit 24. Then, by delay time detecting circuit 24, the time from the instance when the output of pattern generator 21 changes to the instance when current I changes is detected for each bit of the output of pattern generator 21. The delay time of each bit may be detected, for example in FIG. 10, by successively changing potential group (V1, V2, V3) to be supplied to electrodes E1, E2 and E3 to (0, 0, 0), to (15, 0, 0), to (0, 0, 0), to (0, 15, 0), to (0, 0, 0) and to (0, 0, 15).
FIG. 11 shows variation in current I when all of the 1024 multiple beams from blanking aperture array mask 14 are captured by Faraday cup 23 and then, one of the beams is intercepted by aperture stop 15 for a predetermined period of time. Negative pulse 25 indicates the interception time.
However, the SN ratio is low because the variation in current I is small and even if the transmission line from Faraday cup 23 to delay time detecting circuit 24 of FIG. 9 is of high quality, the pulse shape of current I becomes dull, so that the accuracy of the delay time detection decreases.